Azelastine is a phthalazinone derivative having the following structural formula: ##STR1##
The chemical designation is: 4-(4-chlorobenzyl)-2- (perhydro-1-methyl-azepine-4-yl)-1-(2H)phthalazinone. Azelastine is used in particular for prophylactic treatment of asthma. Azelastine also has anti-allergic and antihistamine properties, see German Patent No. 21 64 058.